1. Field of the Invention
This invention relates to a connection method and a connection device for electrical connection of small portions, in particular, various portions in electronic parts, etc.
2. Description of the Related Art
In order to electrically connect the inner lead portion of a lead frame and a bonding pad formed on a semiconductor chip, a wire bonding method using a gold wire or aluminum wire is generally used. Recently, methods of forming a bump on a bonding pad and electrically connecting the bump to the wiring pattern formed on a film cartlet or electrically connecting the bump to the wiring pattern formed on the board as in TAB (tape automated bonding) or flip-chip bonding have been used. With the above methods, the bonding pad and the bonding wire, the bonding wire and the inner lead portion, and the bump and the wiring pattern are electrically connected to each other by metal bonding. Further, soldering is often used for electrical connection at the time of mounting of electronic parts on the printed-circuit board.
However, the wire bonding method has defects that the arrangement of elements formed on the semiconductor chip is limited and it is difficult to reduce the pitch between the pads. That is, in order to connect the bonding wire and the bonding pad to each other by metal bonding, it is necessary to apply a physical load such as heat, pressure or ultrasonic vibration to the connection portion. Therefore, when a semiconductor element is formed in an area directly under the bonding pad, the element may be damaged and the characteristic thereof may be deteriorated. Thus, the semiconductor element cannot be formed in an area near or directly under the bonding pad. Further, since the shortest distance between adjacent bonding wires is limited by the outer diameter of a bonding capillary, it is practically difficult to reduce the pitch between the pads to be less than 100 .mu.m. For this reason, the chip size of a semiconductor chip in which a large number of pads are required to be formed must be increased.
In a connection method using no bonding wire, unlike TAB or flip-chip bonding, a larger amount of heat and a higher pressure may be often applied to the connection portion than in the wire bonding method. For this reason, the elements formed in the semiconductor chip may be often damaged. Further, the pad pitch may be reduced to less than approx. 80 .mu.m, but since it is not preferable to reduce the size of the bump from the viewpoint of the mechanical strength, reduction in the pad pitch is limited. Further, since a large number of bumps and a large number of wiring patterns are connected at the same time, the heights of the bumps must be made constant and the connection position must be precisely determined. Thus, the connection method, such as TAB and flip-chip bonding, has the defects that various conditions for connection are severe, variation in the connection state and connection strength tends to occur and it is difficult to attain the stable connection.
In a case where electronic parts are mounted on the printed-circuit board, for example, where the outer lead portion of the semiconductor device is connected to the wiring pattern formed on the printed-circuit board by soldering, solder must be previously attached to the outer lead portion. Further, flux or the like must be coated on a to-be-connected portion. In addition, it is necessary to remove the flux by using organic solvent after the soldering is completed. Thus, the connection method using solder requires a large number of working steps, the working efficiency is low and the reliability thereof is low. Further, since the organic solvent and solder vapor are harmful, the environmental protection measure must be taken and the manufacturing cost will be increased.